Encapsulation offers benefits to many medicinal applications by providing controlled-release of cargos while facilitating storage, transport and stability of the encapsulated content. To entrap large nanoparticles in hollow shells, two general methodologies have been used. The first general approach is to trap the desired nanoparticles in larger nanoparticles, grow a shell around the larger nanoparticles, and then remove the media between the original nanoparticles and the shells to create the final encapsulation product in hollow shells. The second general approach is to impregnate an existing shell with reactants and grow nanoparticles within the shells and a few examples of this exist.
Smaller nanoparticles have been embedded in larger solid particles. For example, 3-(trimethyoxysilyl) propylmethacrylate (MPS) modified silica particles have been coated with a polymer (Sondi et al., 2000). Polystyrene has been prepared with multiple silica nanoparticles inside (Bourgeat-Lami et al., 1998). Acrylate polymer/silica nanocomposite solid particles have been fabricated through miniemulsion polymerization (Qi et al., 2006). Oleic acid modified silica nanoparticles have been encapsulated in polystyrene by in situ emulsion polymerization (Ding et al., 2004). Fluorescent polymer (PDDF) and Fe3O4 nanoparticles have been trapped inside silica spheres (Lee et al., 2013). Monodisperse silica-coated amorphous cobalt nanoparticles have been produced (Liz-Marzan et al., 2003). Individual Au or Ag nanoparticles have been trapped in polymer particles (Ohnuma et al., 2009). Individual Fe2O3 nanoparticles have been trapped in silica shells (Feyen, 2010). Ag/Au alloy nanostructures have been trapped in polymers (Xing et al., 2010).
A single large nanoparticle has also been placed inside a hollow shell. For example, silica rattle particles with a single mobile silica core have been prepared (Okada et al., 2012). Selective-etching methods for synthesizing silica nanorattles have also been achieved (Chen et al., 2009).
Individual hollow shells have been synthesized, and most approaches for fabrication of hollow structures rely on template-assisted synthesis, using hard (polymer particles) or soft (emulsion or vesicles) templates to form shell structures. Polystyrene particles have been used as sacrificial templates for forming hollow silica shells (Sandberg et al., 2013). Surface-protected etching has also been used to prepare silica shells (Zhang, 2008). Hybrid core-shell particles have also been prepared using monodispersed polystyrene beads as templates (Xia et al., 2004). Hollow silica shells have also been prepared using polystyrene beads as the core and polyethyleneimine (PEI) as a shell template (Mashimo, 2011). Polystyrene-methyl acrylic acid latex has also been used as a template for hollow silica spheres (Ge et al., 2009). Hollow silica spheres have been prepared using water in oil (W/O) emulsion systems (Song et al., 2006). Hollow silica microcapsules have been prepared using a water/oil/water (W/O/W) emulsion (Fujiwara, 2004). Additionally, polystyrene/silica/maghemite composite particles have been prepared (Zhang et al., 2012).
Further, nanoparticles may be grown directly within a shell. For example, rattle-type silica particles with copper cores have been prepared (Koo et al., 2004). Gold cores have also been prepared directly inside hollow silica shells (Nann et al., 2007).
While the above techniques may allow preparation of individual nanoparticles of varying configurations, practical ways for preparing multiple photonic nanoparticles encapsulated within larger hollow nanoparticle shells have yet to be established. The present invention satisfies this need and provides related advantages as well.